Liquefied petroleum gas (LPG) is a fuel liquefied by cooling or pressurizing gas components extracted together with crude oil from an oil field when petroleum is drilled. The LPG includes propane and butane as main ingredients, and has a calorific value higher than those of other fuels.
The LPG is easily liquefied or evaporated, and the volume of the LPG is decreased when the state of the LPG is changed from a gas state to a liquid state. The boiling point of the LPG is about −42° C. When the LPG is liquefied at a room temperature, a volume of propane and a volume of butane in the LPG are decreased by 1/260 and 1/230, respectively, so that the LPG can be conveniently stored and carried.
The LPG is carried by a vessel (particularly, an LPG carrier) from an area of production to an area of consumption. At this time, the vessel has a plurality of liquefied gas storage tanks, and the LPG may be accommodated in a low-temperature liquid state in the liquefied gas storage tanks.
Meanwhile, the vessel supporting the liquefied gas storage tanks may sails along various routes. When a canal exists on a route of the vessel, specifications of the vessel may be limited depending on the size of the canal.
As an example, when the vessel should pass through the old Panama Canal, the width of the vessel cannot exceed 32.3 m, and vessels capable of passing through the old Panama Canal are called as Panamax vessels. However, the new Panama Canal that allows vessels having widths up to 49 m to pass therethrough has recently been opened. Vessels capable of passing through the new Panama Canal are called as new Panamax vessels, and the existing Panamax vessels are called as post Panamax vessels.
The width of a vessel is limited as described above such that the vessel passes through the old Panama Canal. In this case, the total capacity of liquefied gas to be loaded in the vessel cannot help being limited. Hence, only carriers in which the total capacity of liquefied gas is 60K or so sail for the purpose of their safe sailing.